泥页岩井壁稳定研究及在临盘地区的应用

从岩石力学和物理化学两个主要因素简要分析了井壁失稳的机理，指出泥页岩井壁失稳是由力学与化学两方面因素共同作用的结果。钻井液与泥页岩存在化学势差，并改变了井壁附近的孔隙压力，降低岩石强度。借助于井壁处有效应力的变化,将泥页岩与钻井液相互作用时页岩水化所产生的力学效应与纯力学效应结合起来，计算出任意井斜方位井眼围岩应力状态，利用测井资料求出有关岩石力学参数和Mohr Couloumb准则，计算得出防塌的临界钻井液密度。

STUDY ON MUD SHALE STABILITY AND ITS APPLICATION

The unstability mechanism of the wellbore is briefly analyzed from the rock mechanics and chemico-physical factors. It is concluded that shale unstability is influenced by the synergetic effects of mechanic and chemical factors. Chemical potential differential between the drilling fluid and the shale will change the pore pressure adjacent to the well bore, which will reduce the rock strength. This paper has analyzed the sidewall stress status on the basis of changes of effective stresses near the borehole area. By combining the mechanic effects produced by shale hydration and pure mechanic effects, the stresses in the wall rocks at any inclination can be calculated. Then through use of logging data, the critical anti-sloughing drilling fluid density can be calculated according to Mohr-Couloumb rules.